fix(NODE-6878): documents.clear() throws a TypeError after cursor is rewound (#4488)

Co-authored-by: Bailey Pearson <[email protected]>

Author: italojs

src/cmap/wire_protocol/responses.ts

@@ -8,6 +8,7 @@ import {
   parseToElementsToArray,
   parseUtf8ValidationOption,
   pluckBSONSerializeOptions,
+  serialize,
   type Timestamp
 } from '../../bson';
 import { MONGODB_ERROR_CODES, MongoUnexpectedServerResponseError } from '../../error';
@@ -230,11 +231,9 @@ export class CursorResponse extends MongoDBResponse {
    * This supports a feature of the FindCursor.
    * It is an optimization to avoid an extra getMore when the limit has been reached
    */
-  static emptyGetMore: CursorResponse = {
-    id: new Long(0),
-    length: 0,
-    shift: () => null
-  } as unknown as CursorResponse;
+  static get emptyGetMore(): CursorResponse {
+    return new CursorResponse(serialize({ ok: 1, cursor: { id: 0n, nextBatch: [] } }));
+  }
 
   static override is(value: unknown): value is CursorResponse {
     return value instanceof CursorResponse || value === CursorResponse.emptyGetMore;

test/integration/crud/find.test.js

@@ -3,7 +3,7 @@ const { assert: test } = require('../shared');
 const { expect } = require('chai');
 const sinon = require('sinon');
 const { setTimeout } = require('timers');
-const { Code, ObjectId, Long, Binary, ReturnDocument } = require('../../mongodb');
+const { Code, ObjectId, Long, Binary, ReturnDocument, CursorResponse } = require('../../mongodb');
 
 describe('Find', function () {
   let client;
@@ -2388,4 +2388,32 @@ describe('Find', function () {
       });
     });
   });
+
+  it(
+    'regression test (NODE-6878): CursorResponse.emptyGetMore contains all CursorResponse fields',
+    { requires: { topology: 'sharded' } },
+    async function () {
+      const collection = client.db('rewind-regression').collection('bar');
+
+      await collection.deleteMany({});
+      await collection.insertMany(Array.from({ length: 4 }, (_, i) => ({ x: i })));
+
+      const getMoreSpy = sinon.spy(CursorResponse, 'emptyGetMore', ['get']);
+
+      const cursor = collection.find({}, { batchSize: 1, limit: 3 });
+      // emptyGetMore is used internally after limit + 1 documents have been iterated
+      await cursor.next();
+      await cursor.next();
+      await cursor.next();
+      await cursor.next();
+
+      // assert that `emptyGetMore` is called.  if it is not, this test
+      // always passes, even without the fix in NODE-6878.
+      expect(getMoreSpy.get).to.have.been.called;
+
+      cursor.rewind();
+
+      await cursor.toArray();
+    }
+  );
 });